1. Field of the Invention
The present invention relates to a method of welding between a rotor and a shaft and a device for the method, and more particularly to a method of welding between a rotor and a shaft for a turbocharger and a device for the method.
2. Description of the Related Art
A conventional method of welding between a rotor and a shaft related to the present invention is disclosed in Japanese Laid-Open Patent Application No. 60(1985)-118394, published on June 25, 1985. There the method is called condenser-type resistance welding. A device 70 for the method is shown in FIG. 1. In FIG. 1, a shaft 71 of a turbocharger (not shown) is fixed to an upper electrode 72. A rotor 73 of the turbocharger is fixed to a lower electrode 74. The shaft 71 is made of heatproof steel and the rotor 73 is made of heatproof alloy. Both the upper electrode 72 and the lower electrode 74 are connected to a power source (not shown) which comprises a condenser. The shaft 71 comprises a connecting-end 71a. The rotor 73 comprises a center-boss 73a and a connecting face 73b.
The lower electrode 74 is fixed to a stationary holder (not shown). The upper electrode 72 is fixed to a movable holder (not shown). The shaft 71 is pressed down to the rotor 73 by the movable holder.
The shaft 71 and the rotor 73 are welded under the conditions that the charging voltage of the condenser is at 250-300 V, the pressing force of the movable holder is 800-1000 kgf and the time is about 10 seconds. Thus, a connecting portion 75 between the connecting-end 71a and the connecting face 73b is heated up to 1300 degrees centigrade.
Consequently, the shaft 71 and the rotor 73 are welded by the heating and the pressing force.
In the above-mentioned method, electric flux is concentrated at the connecting portion 75, the center-boss 73a and so on. Namely, electric flux is concentrated at a contact portion that different members contact each other at a small area. Since the electric flux and the pressing force are concentrated at the area of the center-boss 73a, there is a possibility that the center-boss 73a is softened and damaged.